1. Field of the Invention
The present invention relates to a plastic cap having a fact-of-opening indicating mechanism, i.e., having tamper-evident (TE) characteristics, which comprises a cap body made up of a top panel and a skirt-like side wall portion hanging down from the peripheral edge of the top panel, and a peripheral band portion provided at the lower end of the skirt-like side wall portion. More specifically, the invention relates to a plastic cap of the type in which the peripheral band portion that exhibits TE characteristics is secured upon engagement with the engaging protrusions such as ratchet pawls formed on the outer peripheral surface of a neck portion of a container at the time of opening the cap.
2. Description of the Prior Art
The plastic cap having TE characteristics has a structure in which a peripheral band portion is formed at a lower portion of the cap body via a weakened line. In a representative example, flexible flap pieces are formed on the inner surface of the peripheral band portion. In opening the cap, the flap pieces engage with the lower side of a jaw portion which is formed along the outer periphery of the neck portion of the container, whereby the peripheral band portion is secured. When the cap body is opened, the weakened line is broken, and the cap body and the peripheral band portion are separated from each other.
In the cap of the above-mentioned type, when the flap pieces that have engaged with the lower side of the jaw portion, the flap pieces are bent and are elongated or the flap pieces themselves undergo elastic elongation. Therefore, the weakened line is not readily broken when the cap is opened. That is, the weakened line may often be broken after it is attempted to open the cap and after the sealing by the cap body at the mouth of the container is removed, which is not satisfactory from the standpoint of TE characteristics.
As a cap that has improved the above-mentioned problem, there has been known the one in which the peripheral band portion is secured at the time of opening the cap not relying upon the engagement between the flap pieces of the peripheral band portion and the jaw portion of the container but relying upon the engagement between the protrusions provided on the inner peripheral surface of the peripheral band portion and ratchet pawls formed on the outer peripheral surface of the neck portion of the container (see Japanese Laid-Open Utility Model Publication No. 131362/1981). In the cap of this type, protrusions indicating the direction in which the cap is opened are provided along the inner peripheral surface of the peripheral band portion maintaining a predetermined distance. In opening the cap, therefore, the protrusions and the ratchet pawls on the outer peripheral surface at the neck portion of the container engage with each other in the circumferential direction, whereby the peripheral band portion is inhibited from rotating and the weakened line is readily broken, effectively solving the problem in that the weakened line is readily broken after the seal at the mouth of the container is removed.
In the cap of this type, however, a problem still remains in that when the cap is closed to tighten the mouth of the container, the protrusions formed along the inner peripheral surface of the peripheral band portion ride over the ratchet pawls at the neck portion of the container exerting a large suppressing force on the band portion, whereby the cap body only is turned in the closing direction and the weakened line is broken. In closing the cap, therefore, it is necessary that the peripheral band portion and the cap body are turned together.
According to the above-mentioned prior art (Japanese Laid-Open Utility Model Publication No. 131362/1981) as shown in FIG. 1 thereof, a suitable gap is formed between the lower end of the skirt-like side wall of the cap body and the peripheral band by coupling them together via a plurality of collapsible bridges 20, and stoppers 22 and 24 are formed on the lower end surface of the skirt-like side wall and on the upper end surface of the peripheral band portion. That is, the stopper 24 of the peripheral band portion is disposed on the side of closing the cap with respect to the stopper 22 on the skirt-like side wall. In closing the cap, therefore, the stopper 22 is readily brought into contact with the stopper 24. Accordingly, the cap body and the peripheral band portion turn together, and the bridges 20 are not broken at the time of closing the cap.
In the above-mentioned cap, however, stoppers 22 and 24 must be formed on the lower end surface of the skirt-like side wall and on the upper end surface of the peripheral band portion and, hence, the gap between the two (length of bridges 20) must be so increased as will be capable of forming stoppers. Therefore, the portion where the lower end surface of the skirt-like side wall and the upper end surface of the peripheral band portion stopper 24 of the peripheral band portion is disposed on the side of closing the cap with respect to the stopper 22 on the skirt-like side wall. In closing the cap, therefore, the stopper 22 is readily brought into contact with the stopper 24. Accordingly, the cap body and the peripheral band portion turn together, and the bridges 20 are not broken at the time of closing the cap.
In the above-mentioned cap, however, stoppers 22 and 24 must be formed on the lower end surface of the skirt-like side wall and on the upper end surface of the peripheral band portion and, hence, the gap between the two (length of bridges 20) must be so increased as will be capable of forming stoppers. Therefore, the portion where the lower end surface of the skirt-like side wall and the upper end surface of the peripheral band portion are coupled together is not formed by the subsequent working such as cutting that is carried out at the time of forming perforation but is formed simultaneously with the formation of the cap as a unitary structure.
In closing the cap, furthermore, the pushing force is directly exerted on the collapsible bridges 20, whereby the gap between the lower end surface of the skirt-like side wall and the upper end of the peripheral band portion is crushed and the bridges tend to be broken. Therefore, in order to prevent the bridges 20 from breaking by the crushing, it has been attempted to provide protuberances (spacer protuberances) between the lower end surface of the skirt-like side wall and the upper end surface of the peripheral band portion, the protuberances being connected to either one of them and extending toward the other side.
As described above, stoppers or bridges are formed in space between the lower end of the skirt-like side wall and the upper end of the peripheral band portion or spacer protuberances are formed therein depending upon the cases. Therefore, the plastic is integrally molded by using a complex metal mold, or a split mold is used by taking the rapping of mold into consideration, imposing limitation on the molding speed which is very unsatisfactory from the standpoint of productivity.